Electric-resistance welded pipe(short for erw pipe
),can only occur under certain circumstances and have the following characteristics:
(1) Stress corrosion cracking occurs only when stress (especially tensile stress) is present. This stress can be applied stress, or residual stress introduced during welding and joining, or expansion stress caused by wedge action of the corrosion product.
(2) Stress corrosion cracking is a time-dependent lag damage that is completely similar to hydrogen hysteresis cracking.
(3) Stress corrosion cracking is a kind of low stress brittle fracture.
Stress corrosion cracking is a common failure of chemical equipment, especially erw pipe
bends. The unpredictability of stress corrosion cracking is the biggest hidden danger in the petrochemical industry. The necessary condition for stress corrosion cracking is the coexistence of tensile stress and corrosive medium, which is an important condition for stress corrosion. In industrial equipment such as petrochemical and nuclear power plants, most of the stress corrosion caused by stress corrosion is caused by residual tensile stress, which is often superimposed on the working stress. The residual tensile stress mainly comes from the residual tensile stress generated by the equipment during the welding process. At present, extensive use of annealing after annealing to eliminate residual stress, welding residual stress is an important process, this method is a waste of energy, easy to produce large welding residual stress. Post-weld heat treatment is a new technique to eliminate residual stress. The material is preheated to the post-heat treatment temperature before welding, and the heat is continuously welded during the welding to maintain the temperature. After welding is completed, heat with a cotton wool and cool slowly. The method can effectively reduce the welding residual stress and improve the stress corrosion resistance of the metal.
After welding, heat treatment can effectively reduce the welding residual stress. The higher the heat treatment temperature, the better the residual stress elimination effect. The heat treatment after welding can also effectively improve the corrosion resistance of the resistance welded pipe. The higher the heat after the heat treatment, the more significant the resistance to stress corrosion.